JPS6171582A - Induction heating cooking device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention generates a high-frequency magnetic field from a heating coil and applies it to a pot, which is a load, to generate an eddy current in the steel, thereby reducing eddy current loss. This invention relates to an induction heating cooker that performs cooking by self-heating of steel based on the above.

[Technical background of the invention and its problems]

Recently, an induction heating cooker that is capable of heating not only iron and 18-8 stainless steel but also aluminum and copper pots has been developed and is already in practical use.

By the way, in such an induction heating cooker, during cooking, the current generated in the pot is in the opposite direction to the current flowing through the heating coil. For this reason, a repulsive force acts between the steel and the heating coil, and if m < (including food) is light, the steel will float off the top plate, and if the top plate is even slightly tilted, the steel will float away from the top plate. It is very dangerous to move from the correct set position.

However, if the steel material has high magnetic permeability like iron, the magnetic force between the steel and the heating coil is large, and a strong attractive force acts there, so even if the above repulsive force occurs, it will not can be ignored and the pot will not move.

However, when the steel material has low magnetic permeability and low resistance, such as aluminum or copper, a large current is passed through the pot in order to increase the input resistance of the heating coil as in the case of steel, so the heating coil and The repulsive force between it and the pot becomes extremely large. Moreover, since aluminum and copper are non-magnetic materials,
There is no movement due to the magnetic attraction. Therefore, if the steel is light, the pot will move on the top plate as described above, which is dangerous. Also, if the steel on the top plate moves from its correct setting position, proper heating will not be possible.
There is a problem in that it has a negative effect on the quality of cooking.

[Purpose of the invention]

This invention was made in view of the above circumstances,
The purpose of this is to be able to stop cooking as soon as the load moves from the correct set position, thereby ensuring safety and ensuring superior safety and reliability by ensuring only proper heating at all times. The purpose of the present invention is to provide an induction heating cooker.

[Summary of the invention]

In this invention, a magnetic sensor is provided near the heating coil, and a detection means is provided for detecting the position of the load with respect to the heating coil based on the output of the magnetic sensor, and based on the detection result of the detection means, a high-frequency current is applied to the heating coil. It controls the operation of the inverter circuit that supplies

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

First, FIG. 2 shows the heating coil and its surroundings viewed from above. In Fig. 2, 1 is a heating coil;
Near, for example, around the heating coil 2, magnetic sensors such as search coils 2, 3.4 are arranged at equal intervals. A top plate (not shown) is provided at a predetermined distance above the heating coil 1 on which a load such as a steel 5 to be described later is placed.

FIG. 1 shows the control circuit.

6 is a commercial AC'R source, and this electricity i! A rectifier circuit consisting of a diode bridge 8 and a smoothing capacitor 9 is connected to the power switch 6 through a power switch 7 and a relay contact 54b in series. A high frequency inverter circuit 10 is connected to the output end of this rectifier circuit, and a heating coil 1 is connected to this high frequency inverter circuit 1o. Here, the high-frequency inverter circuit 10 has a resonant capacitor that forms a resonant circuit together with the heating coil 1, and a high-frequency current is caused to flow through the heating coil 1 by exciting the resonant circuit by turning on and off a switching element. It looks like this. Furthermore, the high-frequency inverter circuit 10 has the ability to detect the phase of the high-frequency current flowing through the heating coil 1 and correct the on/off timing of the switching element according to the detected phase to cause the resonant circuit to stably oscillate. are doing.

In general, a pan position detection circuit 20 is connected to the power source 6 via the power switch 7 and the step-down transformer 11. This pot position detection circuit 20 includes the search coil 2.3.
．． The position of the steel 5 with respect to the heating coil 1 is detected according to the output of the heating coil 1, and the operation of the high frequency inverter circuit 10 is controlled according to the detection result.

Here, a specific example of the pot position detection circuit 20 is shown in FIG.

As shown in FIG. 3, the output of the search coil 2 is rectified by a diode 21 and applied to a parallel circuit of a resistor 22 and a capacitor 23. The voltage Vda of the capacitor 23 is a voltage follower (gain is “1”) 2
4 and a capacitor 25 to an absolute value circuit 26. This absolute value circuit 26 has a resistor 26r on the input side that forms a differential circuit together with the capacitor 25, and when the voltage generated at the resistor 26r changes, it is amplified with the same gain regardless of the positive or negative level. This is what is output. Then, the absolute value circuit 26
The output voltage vOa is supplied to the non-inverting input terminal of the comparator 27.

The inverting input of the comparator 27 is supplied with the reference voltage occurring at the interconnection point of the resistors 28 and 29.

Similarly, the output of the search coil 3 is rectified by a diode 31 and applied to a parallel circuit of a resistor 32 and a capacitor 33. The voltage Vdb of the capacitor 33 is supplied to an absolute value circuit 36 via a voltage follower (gain is "1") 34 and a capacitor 35. This absolute value circuit 36 has a resistor 36r on the input side that forms a differential circuit together with the capacitor 35, and when the voltage generated at the resistor 36r changes, it is amplified with the same gain regardless of the positive or negative level.
This is what is output. The output voltage Vob of the absolute value circuit 36 is supplied to the non-inverting input terminal of the comparator 37. A resistor 3 is connected to the inverting input terminal of the comparator 37.
A reference voltage is provided at the 8.39 interconnection point.

Roughly speaking, the output of the search coil 4 is rectified by a diode 41 and applied to a parallel circuit of a resistor 42 and a capacitor 43. The voltage Vdb of the capacitor 43 is supplied to an absolute value circuit 46 via a voltage follower (with a gain of "1"> 44) and a capacitor 45. It has a resistor 46r forming a differential circuit, and when the voltage generated across the resistor 46r changes, it is amplified with the same gain regardless of the positive or negative level and outputted.Then, the output of the absolute value circuit 46 Voltage VO
C is supplied to the non-inverting input terminal of the comparator 47. A resistor 48.4 is connected to the inverting input terminal of the comparator 47.
A reference voltage occurring at the 9 interconnection points is supplied.

Therefore, the outputs of the comparators 27, 37, and 47 are the OR circuits 5
0, and the output of this OR circuit 50 is supplied to AND circuit 5
1 is supplied to one input terminal of 1. The output of the timer 52 is supplied to the other input terminal of the AND circuit 51. This timer 52 generates a logic "1" signal after a certain period of time (longer than any time constant of the capacitor 25 and resistor 26r) after the power supply 6 is turned on. The output of the AND circuit 51 is supplied to the set input terminal S of the flip-flop circuit 53.

On the other hand, a DC voltage Vcc is applied to the relay 54 via the collector and emitter of an NPN transistor 55. The Q output of the flip-flop circuit 53 is supplied to the base of the transistor 55. Note that a diode 56 for preventing back electromotive force is connected in parallel to the relay 54.

Next, the operation in the above configuration will be explained.

15 on the top plate and turn on the NWA switch 7. Then, the high frequency inverter circuit 10 operates and a high frequency current flows through the heating coil 1. In this way, a high frequency magnetic field is emitted from the heating coil 1 and is applied to the steel 5, causing the pot 5 to self-heat. In other words, cooking is started.

At this time, if the steel 5 is made of aluminum or copper with low magnetic permeability and low resistance, and is also light, the steel 5 will float off the top plate due to the repulsive force caused by the current generated in the heating coil 5 and the current flowing in the heating coil 1. If the top plate is tilted, the pot 5 will move on the top plate. When the pot 5 moves toward the search coils 2 and 4 and away from the search coil 3, the magnetic flux density around the search coil 3 increases, and the output voltage of the search coil 3 increases. Then, as shown in FIG. 4, the voltage Vdb of the capacitor 33 rises, a high-level voltage 1b is generated across the resistor 36r in the absolute value circuit 36, and a high-level voltage VOb is output from the absolute value circuit 36. In this way, the output signal of the OR circuit 50 becomes logic "1".

On the other hand, when a certain period of time has elapsed after turning on the power switch 7, the timer 52 outputs a logic "1°" signal. Therefore, at this time, the output of the OR circuit 50 is a logic "1" signal.
If so, the output of the AND circuit 51 becomes logic "1°", and the flip-flop circuit 53 is set.Then,
Transistor 55 turns on and relay 54 operates. When the relay 54 is activated, the contact 54b is opened, and the energization to the high frequency inverter circuit 10 is stopped, and the operation of the high frequency inverter circuit 10 is stopped. In other words, cooking stops.

In this way, when the pot 5 on the top plate moves from its correct set position, it is immediately detected and cooking is stopped, so that, for example, if the pot 5 moves to the edge of the top plate and touches the user. There is no risk of burns, and heating is prohibited when the pot is likely to fall off the top plate, making it safe. Moreover, pot 5
Continuing to cook with the heater deviated from the correct set position will not allow proper heating and will have a negative impact on the quality of the cooking, but such inconveniences can be prevented and reliability improved. can be achieved.

Furthermore, the timer 52 and the AND circuit 51 maintain the reset state of the flip-flop 53 for a certain period of time after the power switch 7 is turned on, regardless of the output of the OR circuit 50. When, search coil 2.3.4. Even if the output voltage of the OR circuit 50 changes and the output of the OR circuit 50 becomes logic "1", the relay 54 will not be operated unnecessarily. In other words, malfunctions when the power is turned on can be prevented.

Note that in the above embodiment, three Hall elements were used and arranged at equal intervals around the heating coil 1, but there is no limit to the number or the arrangement position, as long as the movement of the pot 5 can be detected. . For example, one search coil may be arranged in the center of the heating coil.

Further, in the above embodiment, a search coil is used as the magnetic sensor, but the present invention is not limited to this, and a Hall element may be used. An example thereof is shown in FIG. That is, 62,
Hall elements 63 and 64 are arranged around the heating coil 1 at equal intervals.

When a voltage is applied between terminals a and b, Hall elements 62, 63, and 64 transmit a Hall voltage to terminals c and d according to the magnetic flux density.
The output of the Hall element 62゜63.64 is half-wave rectified and amplified by the next stage rectification/amplification circuit 76゜86.96, and then sent to the non-inverting input terminal of the comparator 27.37.47. is being supplied to. Therefore, in this case as well, when the steel 5 moves, it is captured by the Hall elements 62, 63, 64 as a change in magnetic flux,
The operation of the high frequency inverter circuit 10 is controlled.

〔Effect of the invention〕

As described above, according to the present invention, a magnetic sensor is provided in the vicinity of the heating coil, and a detection means is provided for detecting the position of the load with respect to the heating coil based on the output of the magnetic sensor. Based on this, the operation of the inverter circuit that supplies high-frequency current to the heating coil is controlled, so that cooking can be stopped immediately when the load moves from the correct set position.This not only ensures safety, but also ensures proper cooking at all times. It is possible to provide an induction heating cooker with excellent safety and reliability that enables only accurate heating.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a control circuit according to an embodiment of the present invention, FIG. 2 is a diagram of the heating coil and its surroundings seen from above in the same embodiment, and FIG. 3 is a detailed diagram of the main parts of FIG. 1. FIG. 4 is a diagram for explaining the operation of FIG. 3, and FIG. 5 is a diagram of the main part of a control circuit showing another embodiment of the present invention. 1... Heating coil, 2.3.4... Search coil (
magnetic sensor), 5...lI (negative v1), 20... rough position detection circuit, 54... relay. Applicant's agent Patent attorney Takehiko Suzue Q9'-Sun

Claims (2)

[Claims] (1) A heating coil, an inverter circuit that supplies a high-frequency current to the heating coil, a magnetic sensor provided near the heating coil, and detection for detecting the position of the load with respect to the heating coil based on the output of the magnetic sensor. means and
An induction heating cooker comprising: control means for controlling the operation of the inverter circuit according to the detection result of the detection means. (2) The induction heating cooker according to claim 1, wherein the control means controls the operation of the inverter circuit according to the detection result after a certain period of time after power is turned on.